Joan found a class for me in the Cambridge Center for Adult Ed catalog on the subject of sharpening blades and scrapers. It was taught by a wood artisan, Dan Paret, who uses mainly hand tools in his work. As it turns out, we are friends with him and his wife, though we have not seen them in a few years.

Even though I have not completed my experiments with Brent’s methods, I decided to take the class. It was six hours on a Saturday for $130 and recommended bringing one new chisel and one new scraping card. I brought in my old used chisels and plane irons, but only really got to sharpen two planes. Kind of what I expected. The rest I can do at home for practice.

Dan has been teaching various woodworking classes at Cambridge Center for Adult Education in Harvard Square for 13 years. A guy in the class has taught portrait painting there for 15 years. As it turns out, I taught there for 10 years, too, from 1983-1993: Thai cooking.

Dan’s approach is to keep things as simple as possible so that one is more inclined to sharpen more often, thus using tools that are more sharp. He suggests that sharpening more often is less work than starting from tools that need correction.

Overall, learning by reading makes as much sense for sharpening as for dancing: it’s really hard to get it right without a teacher showing you some techniques, although anything you make up that works is just fine, too. This blog entry is as much for my future reference as it is for others to learn from.

Sharpening Blades

He said the most important thing in sharpening blades is the word FLAT. Flat backs, flat tops, no rounding. The exception is his technique of using a power grinder to create a hollow on the bevel side. More on this later.

Equipment

Like Brent's Sharpening pages, Dan uses abrasive sheets on glass, rather than oil stones, water stones, etc. Unlike Brent, he uses no water or oil on the sheets, and uses sandpaper rather than film.

He has glass plates mounted on masonite with 320 grit sandpaper on the top via adhesive, and 80 grit on the bottom. The top sandpaper is only to provide resistance for sharpening sheets placed on top, which are not glued down; he never uses the 320 that he glued down to sharpen, so there is no need to replace it regularly. He said that 320 is the coarsest grade he has found that will not telegraph its grits to the paper used on top of it. The 80 grit on the bottom is to keep the glass plate and its masonite from sliding on the bench.

He uses 9×11” sheets of sandpaper cut into four 2 3/4” strips, grades 220, 400, 1000, and 2500 when sharpening new blades. He uses 120 or 150 for blades that are seriously unflat on the bottom.

A 6-inch grinder with #36 wheel running at 1200 RPM (or less) is used for grinding a hollow into the bevel face, see below.

Cleaning the Blade

If the chisel or plane iron has any oil or grease on it, wipe it clean with denatured alcohol.

Flattening the Bottom

He suggested that we start by flattening the bottom. One could also start by sharpening the bevel (see below) in some cases.

He put a strip of 220 onto the 320 paper on glass (see equipment, above) then held a chisel perpendicular to the strip, using fingers of both hands to hold it (don’t try to hold it with the handle). Then, make strokes for the length of the sandpaper by moving your body, not your arms. Hold it flat while doing this. You only need to do this to the first inch of the blade, but no harm in doing more. You’re done (about 30 strokes for a new chisel) when the sandpaper lines you put in it are the only thing you can see – no other lines from the original.

This was then repeated for 400, 1000, and 2500. The 2500 gave it a near mirror finish, but he cautioned us that shiny does not mean flat, and flat is what is needed.

Grinding a Hollow in the Front Bevel

I’ve never heard of this before. He suggests using a slow-ish grinder (1200 rpm or less) and a 36-grit 6 inch wheel to grind a bevel. You need an angle guide such as the Veritas one to do this well. You want to adjust the angle so that the initial hollow is midway between the cutting edge and the end of the front bevel. To find that: estimate, flick the motor on then off, and move the chisel into the slowly-moving wheel, just enough to find out where it touches. If it is not in the middle, adjust, try again, and repeat until centered.

Now turn on the motor. Feed the bevel to the wheel until it just touches, with the edge of the chisel in just a bit from the edge of the grinding wheel. Using your fingers as a guide on the bottom of the angle jig to maintain the amount of the feed, move it from right to left and back, once, and stop. Avoid overheating and thus losing temper. It’s easy to overheat an edge if the edge of the bevel is near the edge of the wheel, so avoid that. If it starts to get hot, dip in water then wipe off.

You want to continue doing this until the hollow goes all the way from the edge to the end of the bevel. Look at the edge under a bright light. If it reflects (you have to turn it to find it, but try perpendicular to your face), then it’s too thick, and you’ll spend too much time honing. Repeat the grinding procedure above until you cannot find the edge, because it is too narrow to reflect light back at you.

Why? Two reasons:

The hollow makes two raised edges at the ends of the arc that should both be in contact with the sanding paper with equal pressure. This serves as your guide while honing.

If you are restoring a chipped blade, you will start by jointing the edge flat, and the result will be an edge thicker than a screwdriver. So grinding a hollow means you have a reasonably good edge before honing.

Honing the Bevel

Put a piece of 220 on the 320-faced glass sheet. Make about four strokes (two up , two back) the entire length of the sandpaper, holding the hollowed bevel so that both ridges at the ends of the hollow are in contact with the sandpaper. Hold the chisel with your fingers and thumbs, with the blade 90 degrees from the length of the sandpaper strip you’re using. Keep the angle of the chisel to the glass surface the same while you do it; avoid lifting the chisel handle, which will round your edge.

Check for a burr on the back. When the burr is even all the way across, you’re done with 220. Now repeat with 400, 1000, 2000.

He does not use jigs to hold the angle. Instead, he grinds a hollow using a 6” grinder, and the edges of the arc are used as a guide. The downside is that eventually you will sand away the arc and have to hollow it again.

It is tricky to hold the blade just right while honing. For this reason, there is an infinite parade of jigs, commercial and shop-made, for holding the blade at a constant angle. I think the hollow shoulders work fine for chisels, but since a plane iron is much thinner, I’ll make some of Brent's guides.

When finished, turn the chisel over and give it a few couple of strokes at 2500 to remove the burn, then test the chisel.

Restoring a Chipped Blade

I had a chisel in sorry shape. I don’t know where it came from, but it represented a good challenge. It had a pretty good chip in the blade, and the metal was rough from a bit of corrosion (dirt, a bit of paint, some light rust, but not deep rust).

I started by sanding all surfaces, going 120-150-220-400-1000-2500 – the back, the flat of the front, the side bevels, basically all edges except the front bevel itself, which I left as it was.

Then I fed the chisel into a dressed 36-grit wheel at 1200 rpm, checking it to see when the chip area was flat again. Made sure it did not get to hot by pausing or dipping from time to time. Eventually, the chip was gone (checked with a square, also to make sure it was at a right angle with the blade), but the cutting edge was about as thick as a blunt screwdriver. That will last a real long time that way, even with hard strikes, but it won’t cut very well. Creating a hollow, as described above, was the solution. It took time and patience, but eventually the cutting edge was too thin to reflect light.

By the way, Dan didn’t teach me this: I just figured it out and did it after sharpening the first chisel; I wanted more of a challenge. He said that if there is a secondary bevel on the back of a chisel, it’s best to restore flatness using the method above, rather than trying to sand the back flat.

Next Time: Turning a New Burr on a Scraper

Aside from chisels, he also taught how to sharpen and use a scraping card, using a burnisher, flat file, and 1000 / 2500 sandpaper. I’ll talk about that next time.

2 comments so far

like anything – practice makes perfect. the hollow grind is a great way to get a “jig” for practicing with as it aids in keeping the blade at the desired angle. once you get the hang of it and the muscle memory to sharpen it freehand like that, hollow grind or no hollow grind you’ll be able to sharpen freehand more easily.

if you do run into issues of the blade snagging or tipping over/under, try rotating the blade 45 degrees to the line of motion that will give you less forces against the bevel that could tip it off of it’s angle.